Breinholt V, Larsen J C
Institute of Food Safety and Toxicology, Division of Biochemical and Molecular Toxicology, The Danish Veterinary and Food Administration, Morkhoj Bygade 19, 2860 Soborg, Denmark.
Chem Res Toxicol. 1998 Jun;11(6):622-9. doi: 10.1021/tx970170y.
A newly developed recombinant yeast strain, in which the human estrogen receptor has been stably integrated into the genome of the yeast, was used to gain information on the estrogenic activity of a large series of dietary flavonoids. Among 23 flavonoids investigated, 8 were found to markedly stimulate the transcriptional activity of the human estrogen receptor in the yeast assay increasing transcriptional activity 5-13-fold above background level, corresponding to EC50 values between 0.1 and 25 microM. Five compounds increased the transcriptional activity 2-5-fold over the control, with EC50 values ranging from 84 to 102 microM, whereas the remaining flavonoids were devoid of activity. The most potent flavonoid estrogens tested were naringenin, apigenin, kaempferol, phloretin, and the four isoflavonoids equol, genistein, daidzein, and biochanin A. With the exception of biochanin A, the main feature required to confer estrogenicity was the presence of a single hydroxyl group in the 4'-position of the B-ring of the flavan nucleus, corresponding to the 4-position on phloretin. The estrogenic potency of the flavonoids was found to be 4 000-4 000 000 times lower than that observed for 17beta-estradiol, when compared on the basis of EC50 values. The estrogenic activity of the dietary flavonoids was further investigated in estrogen-dependent human MCF7 breast cancer cells. In this system several of the flavonoids were likewise capable of mimicking natural estrogens and thereby induce cell proliferation. Similar structural requirements for estrogenic activity were found for the two assays. The present results provide evidence that several of the flavo-estrogens possess estrogenic properties comparable in activity to the well-established isoflavonoid estrogens. The use of Alamar Blue, a vital dye which is metabolically reduced by cellular enzymes to a fluorescent product, was found to greatly simplify the MCF7 cell-based estrogen screen, making this mammalian assay applicable as a large-scale screening tool for estrogenic compounds.
一种新开发的重组酵母菌株被用于获取有关大量膳食黄酮类化合物雌激素活性的信息，该菌株已将人类雌激素受体稳定整合到酵母基因组中。在所研究的23种黄酮类化合物中，有8种在酵母试验中显著刺激人类雌激素受体的转录活性，使转录活性比背景水平提高了5至13倍，对应的半数有效浓度（EC50）值在0.1至25微摩尔之间。5种化合物使转录活性比对照提高了2至5倍，EC50值在84至102微摩尔之间，而其余黄酮类化合物则无活性。所测试的最有效的黄酮类雌激素是柚皮素、芹菜素、山奈酚、根皮素以及4种异黄酮类化合物：雌马酚、染料木黄酮、大豆苷元和鹰嘴豆芽素A。除鹰嘴豆芽素A外，赋予雌激素活性的主要特征是在黄烷核B环的4'-位存在单个羟基，这与根皮素的4-位相对应。基于EC50值进行比较时，发现黄酮类化合物的雌激素效力比17β-雌二醇低4000至4000000倍。在雌激素依赖的人MCF7乳腺癌细胞中进一步研究了膳食黄酮类化合物的雌激素活性。在这个系统中，几种黄酮类化合物同样能够模拟天然雌激素，从而诱导细胞增殖。两种试验对雌激素活性的结构要求相似。目前的结果提供了证据，表明几种黄酮类雌激素具有与成熟的异黄酮类雌激素相当的雌激素活性。发现使用阿拉玛蓝（一种活体染料，可被细胞酶代谢还原为荧光产物）能大大简化基于MCF7细胞的雌激素筛选，使这种哺乳动物试验可作为雌激素化合物的大规模筛选工具。
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